A variety of diseases exist which require regular treatment by injection of a medicament. Such injection can be performed by either medical personnel or by patients themselves. As an example, type-1 and type-2 diabetes can be treated by patients themselves by injection of insulin doses once or several times per day. It is known to couple a supplemental device to an insulin injection device for recording information about the doses which are administered. Supplemental devices may be used to record dose history information such as the various times at which insulin is administered and the quantity of insulin administered at each such time.
Although electronically recording dose history information addresses the problem of inaccurately recording such information manually, it has the disadvantage of providing a false representation of how much medicament a patient actually injects themselves with. In particular, before administering an injection a patient may eject a small amount of medicament in a so-called prime shot to remove air from within the needle. Supplemental devices configured to record how much medicament is ejected from an injection device may be operable to record both amounts of medicament ejected during prime shots in addition to amounts of medicament that are actually injected into a patient. It will thus be appreciated that simply recording how much medicament is ejected from an injection device does not give an accurate determination of how much medicament is actually injected into a patient. Not knowing such information within an acceptable degree of tolerance may have potentially serious consequences if a patient is subsequently over or under prescribed medication on the basis of an incorrect understanding of how much medicament has previously been injected.
Injection devices such like pen-type injectors also typically comprise a last dose limiting mechanism in order to prevent setting of a dose that would exceed the amount of medicament left in a cartridge. Such last dose limiting mechanisms are typically mechanically implemented, for instance by a last dose limiting member threadedly engaged with a sleeve or rod that is exclusively rotatable during a dose setting procedure but which is rotationally fixed and in non-rotative engagement with a housing of a device during dose dispensing or dose delivery. In addition to gather information about the total amount of medicament injected into a patient it is desirable to obtain precise information about a residual filling level of a cartridge actually in use. Especially when a supplemental device is equipped with a display, information about the quantity and amount of medicament left in a cartridge could be visually displayed or audibly communicated to a user.
Gathering of information related to the actual device status, such like information about a total amount of medicament delivered or a residual amount of medicament left in a cartridge is quite tricky and elaborate when the delivery device is implemented all mechanically and when the supplemental device should be detachably connectable to the injection device.